Geology of Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 46

Coarser
grained layer
Finer grained
layer
FIGURE 2.24
An example of sediment layer variability over short distances. (Photo by Daniel T. Rogers.)
• Even parallel
• Even discontinuous parallel
• Wavy parallel
• Wavy nonparallel
• Discontinuous wavy parallel
• Discontinuous wavy nonparallel
• Discontinuous curved parallel
• Curved nonparallel
• Structureless
• Mottled
• Brecciated
• Algal
• Graded
• Cross
Parallel horizontal bedding is characterized by distinct beds or laminae, with either sharp
or gradational boundaries that are continuous and parallel. This type of stratification is the
most common in fine-grained sediments such as silts and clays. Figure 2.24 is an example
of this type of bedding. Discontinuous , but even parallel stratification is closely related and
represents a stratification of slightly less uniformity.
Wavy stratification may be parallel, nonparallel, or discontinuous and is predominantly
formed by small ripples of silt and sand. When these particles are interbedded with fine-
grained material, they are called flaser bedding. Wavy bedding of all types is an indica-
tion of higher energy and implies a small but discontinuous micro-relief on the bottom
where the sediment accumulates. Discontinuous wavy, nonparallel bedding is a less orderly
arrangement and probably represents a higher level of current flow. Curved parallel or
curved nonparallel bedding are locally present in many fine-grained sediments such as clays,
and probably indicates lateral accretion in channel scours.